Photoionization and photofragmentation in mass spectrometry with visible and UV lasers

Abstract

Ever since the introduction of laser technology to the field of mass spectrometry, several disciplines evolved providing solutions to challenging scientific and analytical tasks in research and industry. Among these are techniques involving multiphoton ionization such as Resonance‐Enhanced Multiphoton Ionization (REMPI, R2PI) and Mass‐Analyzed Threshold Ionization (MATI) spectroscopy, a variant of Zero Kinetic Energy (ZEKE) spectroscopy, that possess the ability to selectively ionize certain preselected compounds out of complex mixtures, for example, environmental matrices, with a high level of efficiency. Another key feature of multiphoton ionization techniques is the ability to control the degree of fragmentation, whereas soft ionization is most highly appreciated in most applications. In cases where rich fragmentation patterns are desired for diagnostic purposes, Photodissociation mass spectrometry (PD‐MS) is applied successfully. PD‐MS allows for the cleavage of selected chemical bonds. With the introduction of chromophoric labels in PD‐MS, it became possible to target certain molecules or groups within a molecule. In this review article, an overview of the basic principles and experimental requirements of REMPI and MATI spectroscopy and PD mass spectrometry are given. By means of selected examples, the latest developments and application possibilities in this field over the past decade with special focus on the German research landscape are pointed out. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 38: 202–217, 2019.

Spatially Shaped Laser Pulses for the Simultaneous Detection of Polycyclic Aromatic Hydrocarbons as well as Positive and Negative Inorganic Ions in Single Particle Mass Spectrometry

“…Pure gas-phase REMPI with the parameters of our REMPI-beam is virtually fragment-free. 37 In a LD-REMPI approach, the degree of fragmentation is consequently determined by the internal energy that the particle acquires from laser desorption. 36 In our setup, the intense LDI beam intersects a fraction of the desorbed plume, contributing additional fragment signals to the spectra.…”

Resonance-enhanced detection of metals in aerosols using single-particle mass spectrometry

“…For example, the particle's humidity and its main composition can have a strong effect on the detection of particle compounds (Neubauer et al, 1998), known as matrix effects. These effects are associated with several poorly determined interactions at the particle surface and in the desorbed plume affect ion formation (Reilly et al, 2000;Reinard and Johnston, 2008;Hinz and Spengler, 2007;Murphy, 2007;Wade et al, 2008;Hatch et al, 2014;Schoolcraft et al, 2000), reduce detection efficiencies, and complicate quantification approaches (Healy et al, 2013;Gemayel et al, 2017;Gross et al, 2000;Fergenson et al, 2001;Qin et al, 2006;Zhou et al, 2016;Shen et al, 2019). These difficulties can be mitigated if the desorption and ionization are separated in a two-step process and ions are formed in the gaseous plume as demonstrated for aromatic hydrocarbons (Morrical et al, 1998;Bente et al, 2008;Woods et al, 2001).…”

“…These difficulties can be mitigated if the desorption and ionization are separated in a two-step process and ions are formed in the gaseous plume as demonstrated for aromatic hydrocarbons (Morrical et al, 1998;Bente et al, 2008;Woods et al, 2001). In such a two-step approach, thermal or laser desorption (LD) is often followed by resonance-enhanced multiphoton ionization (REMPI), a gas-phase ionization technique that is highly sensitive and selective for aromatic molecules (Gunzer et al, 2019). The LD-REMPI approach yields detailed mass spectra of the health-relevant polycyclic aromatic hydrocarbons (PAHs) -ubiquitous trace compounds of combustion particles (Bente et al, 2009;Li et al, 2019;Passig et al, 2017;Schade et al, 2019).…”

Resonance-enhanced Multiphoton Ionization Time-of-Flight Mass Spectrometry for Evaluating Emulsion Inversion via Temperature Change

“…Recently, we reported on the online monitoring of constituents in an emulsion using resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS). [12][13][14][15][16] REMPI has superior optical selectivity and produces fewer fragment ions, [17][18][19][20] which allows for the sensitive detection of a molecular ion within a mixture. TOFMS is a reasonably straightforward non-scanning type MS that allows the simultaneous detection of all induced ions, even when several types of analytes are present in a sample.…”